1. Statement of the Technical Field
The inventive arrangements relate generally to methods and apparatus for providing increased design flexibility for RF circuits, and more particularly to an RF waveguide switch.
2. Description of the Related Art
A waveguide is a transmission line structure that is commonly used for microwave signals. A number of different waveguide structures are known to those skilled in the art. For instance, a waveguide can simply consist of a hollow tube made of an electrically conductive material, for example copper, brass, steel, etc. Such a waveguide can be provided in a variety of shapes, but most often has a rectangular or circular cross section. A coplanar waveguide is a type of waveguide having a conductor disposed between, and coplanar with, two ground planes. The conductor and ground planes are typically coupled to a dielectric.
As with most other types of electrical circuits, it is often required that a microwave circuit have switches. There are three basic RF and microwave switching technologies currently available, namely electromechanical, ferrite and diode. Electromechanical microwave switches typically are mechanically operated and have low insertion loss and VSWR""s of 1.1:1 or better, but switching speed is slow, the switches have a limited life rating, and some of these switches are not practical for hot switching. Hot switching, which is switching while a signal is applied to a switch, can be problematic because voltage reflections can occur while the switch is being operated. Such voltage reflections can damage the circuits with which the switches are used.
Ferrite switches have faster switching speeds than electromechanical waveguide switches, but the VSWR of ferrite switches is not as good as the electromechanical switches. Also, some ferrite switches can have a limited frequency range and/or power handling capability. Diode switches can provide extremely fast switching speeds and are available in very compact packages. However, diode switches have relatively high insertion loss and lower isolation than electromechanical and ferrite switches. Further, the bandwidth of diode switches is fairly narrow. Some of these parameters can be selectively improved, but usually at the sacrifice of other performance parameters.
The present invention relates to an RF switch which includes a waveguide structure having at least a first and second port. The RF switch also includes a dielectric structure defining at least a first cavity disposed at a juncture between the first and second ports. The dielectric structure can define a plurality of elongated fluid cavities at the juncture extending between opposing walls of the waveguide structure.
The RF switch also can include a fluid control system that moves a conductive fluid into the first cavity in a first operational state and at least partially purges the conductive fluid from the first cavity in a second operational state. A conductive path can be provided between the conductive fluid and at least one wall of the waveguide structure.
A low loss RF path is formed between the first port and the second port in the first or second operational state and the first port is substantially isolated from the second port in a different one of the first and second operational states. For example, the low loss RF path can be formed between the first port and the second port in the first operational state and the first port is substantially isolated from the second port in the second operational state.
The waveguide structure also can include a third port and a second dielectric structure can define at least a second cavity disposed at a juncture between the third port and the waveguide structure. The fluid control system can move the conductive fluid into the second cavity in the second operational state. A low loss RF path can be formed between the first port and the third port in the first or second operational state, and the first port and third port can be substantially isolated in a different one of the first and second operational states. The first and second dielectric structure can be integrally formed as a single unit.
The present invention also relates to a method for controlling a path of an RF signal. The method includes the step of providing a low loss RF path between at least a first and second port of a waveguide in a first operational state. In a second operational state the first port is substantially isolated from the second port by selectively transferring a conductive fluid into at least one cavity of a first dielectric structure within the waveguide. For example, the conductive fluid can be transferred into a plurality of fluid conduits defined within the dielectric structure and extending between opposing walls of the waveguide. A spacing between adjacent ones of the fluid conduits can be selected so as not to exceed about {fraction (1/10)} of a wavelength at the operating frequency of the waveguide.
In the first operational state, the first port and a third port of the waveguide can be substantially isolated by transferring the conductive fluid into at least one cavity of a second dielectric structure within said waveguide. In the second operational state, a low loss RF path can be formed between the first port and the third port by at least partially purging the conductive fluid from cavity of the second dielectric structure. The first and second dielectric structures can be formed as a single structure.